Sprinkle remaining teaspoon salt and 1/4 teaspoon pepper on all sides of tuna steaks. Brush wine-and-vinegar mixture on tops and sides of steaks and place, glazed side down, on grill. Grill, brushing with more glaze, until lightly charred, about 3 minutes per side for rare, 6 to 7 for well done. Transfer to serving platter with beans. Add basil to tomatoes, toss, and spoon over tuna. Serve immediately.